This invention relates to an electrophotographic printing machine, particularly but not exclusively a xerographic copier, having a transfer zone at which a developed toner image is transferred from a moving image retaining member to a copy sheet, and means for cleaning residual toner material from the image retaining member after image transfer.
Conventionally, in the automatic xerographic process, a latent electrostatic image of an original to be reproduced is recorded upon an image retaining member and the image then made visible, or developed, by means of a finely divided particulate toner material. In reusable xerography, the developed toner image is generally transferred from the image retaining member to a copy sheet, such as paper or the like, and the image affixed thereto to form a permanent record of the original input scene information. Although a preponderance of the toner material comprising the developed image is transferred to the copy sheet, a small amount of residual toner is nevertheless invariably left behind on the image retaining member surface after the transfer operation. In order to restore the image retaining member to conditions suitable for reuse, the residual toner must be cleaned or removed from the image retaining member surface before a new imaging cycle is instituted.
The cleaning of the image retaining member may be accomplished in a number of different ways. One prevalent technique is to separate the residual toner from the image retaining member by means of an elastomeric blade element as disclosed in U.S. Pat. No. 3,660,863 to Gerbasi. In the blade cleaning process, the cutting edge of the blade is arranged to move between the residual toner particles and the surface of the image retaining member to chisel or cut the toner particles therefrom. Generally, the residual toner is collected in a chamber where it may either be stored for later disposal or recirculated for further use.
A problem may arise however because the copy sheets may have loose particles of debris on their surface. In particular, in the case of paper, paper fibres may be scrubbed or dislodged from the surface by the mechanism which feeds and advances them towards the transfer station, for example a friction retard system paper feeder frequently used in xerographic copiers. These paper fibres and other debris are then prone to collect on the surface of the image retaining member especially at the transfer zone. The debris is conveyed by the moving image retaining member towards the cleaner blade where particles of the debris may become lodged between the image retaining member and the cleaner blade thereby impairing the toner cleaning capability.